Transmitters for wireless networks modulate carrier signals to encode information into a transmitted signal. Transmitters configured to operate in accordance with the 802.11x family of standards employ Gray-coded 22m-QAM (quadrature amplitude modulation) constellation mapping to encode information onto carrier signals.
A typical IEEE 802.11x transmitter comprises a convolution encoder, an interleaver, and a mapper. The encoder incorporates an error-correcting code into an input signal, the interleaver permutes the coded bits in a pre-determined way, and the mapper maps the interleaved bits to symbols in the constellation diagram for modulating the transmission signal.
A new standard, IEEE 802.11p, has recently been defined. This standard is designed for vehicular networks, where the density of users will be high. Consequently, it is desirable to reduce the transmit power of signals, to minimise interference in the dense user environment.